Referring to FIG. 1, a heads-up display 10 typically generates a virtual image of one or more gauges, e.g., a speedometer and an odometer (not shown), for viewing by an operator 12 of a vehicle such as an automobile 14. The term “heads up” indicates that the operator 12 need not lower his gaze to a dashboard 16 to view the gauges. That is the operator 12 can keep his head up and his “eyes on the road” while viewing the gauges. Therefore, the display 10 is an added convenience that also increases the level of safety with which the operator 12 can operate the vehicle 14.
In operation, the heads-up display 10 generates and projects the virtual image of the one or more gauges (not shown) onto a windshield, i.e., a wind screen 18, which reflects the image into the eyes 20 of the operator 12 such that the image appears within the operator's field of view (FOV), sometimes appearing to be at some apparent distance beyond the wind screen. For example, the display 10 may include a light-emitting-diode (LED), liquid crystal (LCD), vacuum fluorescent, or other display technology (not shown) for generating the image; and an optical train (not shown in FIG. 1) for projecting the image onto the wind screen 18.
Typically, the operator 12 is best able to view the virtual image while his eyes 20 are within a three-dimensional viewing space 22, which is sometimes called an eye box. Although the dimensions (e.g., height, width, and/or depth) of the viewing space 22 are typically fixed, they are typically sufficient to accommodate the anticipated ranges of up-and-down, side-to-side, and front-to-back movements of the operator's head 20 while the operator is operating the automobile 14. Furthermore, because the range of operator heights is relatively large (e.g., 5 feet tall-7 feet tall), the display 10 may allow the operator 12 to adjust the vertical position of the viewing space 22 so as to align the viewing space with the operator's eyes 20.
Unfortunately, the typical heads-up display 10 may have several shortcomings. For example, the display 10 may be relatively bulky, and may consume a relatively large amount of power. Furthermore, the quality of the virtual image within the viewing space 22 may be poor. Moreover, because each wind screen 18, even for the same model car, may be slightly different than every other wind screen, the procedure for calibrating the display 10 for each new vehicle may be relatively complex, and may include physically modifying or replacing one or more parts of the display, or perhaps either replacing the entire heads-up display or wind screen. Furthermore, if one ever needs to repair or replace the windscreen, the need to recalibrate the display 10 by modifying or replacing a part or all of the display may significantly increase the time and expense required for an otherwise ordinary repair.